Video encoding/decoding method, apparatus, and recording medium having bitstream stored thereon
An image encoding/decoding method is provided. An image decoding method of the present invention may comprise deriving an intra-prediction mode of a current luma block, deriving an intra-prediction mode of a current chroma block based on the intra-prediction mode of the current luma block, generating a prediction block of the current chroma block based on the intra-prediction mode of the current chroma block, and the deriving of an intra-prediction mode of a current chroma block may comprise determining whether or not CCLM (Cross-Component Linear Mode) can be performed for the current chroma block.
1. A method of decoding an image, comprising:
determining an intra prediction mode of a chroma block; and
generating a prediction block of the chroma block by performing prediction based on the intra prediction mode of the chroma block,
wherein the determining of the intra prediction mode of the chroma block includes: determining whether or not CCLM (Cross-Component Linear Mode) is available for the chroma block based on the chroma block and a luma block related to the chroma block being blocks partitioned in a single tree structure, and
wherein the generating of the prediction block of the chroma block includes: deriving a linear model of the CCLM based on a plurality of reconstructed neighboring samples of the luma block when it is determined that the CCLM is applied to the chroma block.
2. The method of claim 1 , wherein whether or not the CCLM is available for the chroma block is determined based on a type of a slice to which the chroma block belongs.
3. The method of claim 1 , wherein whether or not the CCLM is available for the chroma block is determined based on a size of the luma block.
4. The method of claim 1 , wherein whether or not the CCLM is available for the chroma block is determined based on a size of a coding tree block.
5. The method of claim 1 , wherein the linear model of the CCLM is derived based on sample values obtained by downsampling the plurality of the reconstructed neighboring samples of the luma block.
6. The method of claim 5 , wherein the deriving of the linear model includes: deriving a representative luma sample based on a statistical value of a portion of the reconstructed neighboring samples corresponding to a chroma sample.
7. The method of claim 5 , wherein a parameter of the linear model is derived based on a maximum value and a minimum value which are derived from the sample values.
8. The method of claim 7 , wherein the maximum value is derived as an average of a first maximum value and a second maximum value among the sample values, and the minimum value is derived as an average of a first minimum value and a second minimum value among the sample values.
9. The method of claim 1 , wherein the determining of the intra prediction mode of the chroma block further includes:
determining whether or not the intra prediction mode of the chroma block is a DM (direct mode) based on a first bin of a syntax element related to the intra prediction mode of the chroma block when it is determined that the CCLM is not applied to the chroma block; and
determining the intra prediction mode of the chroma block based on two bins following the first bin of the syntax element when the first bin indicates that the intra prediction mode of the chroma block is not the DM.
10. The method of claim 9 , wherein the intra prediction mode of the chroma block is determined to be one of a Planar mode, a DC mode, a Horizontal mode, a Vertical mode and a vertical-diagonal mode based on the two bins.
11. The method of claim 1 , further comprising:
deriving a value of a first flag indicating whether an MPM mode is applied for the luma block;
deriving, based on the value of the first flag, a value of a second flag indicating whether an intra prediction mode of the luma block is a Planar mode;
deriving, based on the value of the second flag, the intra prediction mode of the luma block;
generating a prediction block of the luma block by performing an intra prediction for the luma based on the intra prediction mode of the luma block,
wherein the deriving the value of the second flag is performed based on whether a reference sample line used for the intra prediction of the luma block is a first reference sample line directly adjacent to the luma block.
12. A method of encoding an image, comprising:
determining an intra prediction mode of a chroma block; and
generating a prediction block of the chroma block by performing prediction based on the intra prediction mode of the chroma block,
wherein the determining of the intra prediction mode of the chroma block includes:
determining whether or not CCLM (Cross-Component Linear Mode) is available for the chroma block based on the chroma block and a luma block related to the chroma block being blocks partitioned in a single tree structure, and
deriving a linear model of the CCLM based on a plurality of reconstructed neighboring samples of the luma block.
13. A non-transitory computer readable recording medium storing a bitstream generated by an image encoding method, the image encoding method comprising:
determining an intra prediction mode of a chroma block; and
generating a prediction block of the chroma block by performing prediction based on the intra prediction mode of the chroma block,
wherein the determining of the intra prediction mode of the chroma block includes:
determining whether or not CCLM (Cross-Component Linear Mode) is available for the chroma block based on the chroma block and a luma block related to the chroma block being blocks partitioned in a single tree structure, and
deriving a linear model of the CCLM based on a plurality of reconstructed neighboring samples of the luma block.